A jailbreak is the act of hacking the iOS operating system to gain access to functions off limits to the user. This gives owners of Apple mobile devices full control over the file system, and lets them install programs from third-party sources. The purpose of modifying iOS is to expand iPhone/iPad/iPod functionality with the aid of unauthorized software vendors and the use of pirated software.

Apple asserts that jailbreaking is illegal and, with the release of iOS 11, has closed nearly all the loopholes.